pga280 zerø-drift, high-voltage, programmable gain ...rr i/o, 5v single-supply ina333...

Gain

Network

ADC

(ADS1259)

+5V

+15V -15V

Switch

Matrix

and

100 A

Source

Sink and

Buffer

m

Control Register7xGPIO SPI Interface

INP2

INN2

INP1

INN1

Address

MUX

SPI

PGA280

Product

Folder

Order

Now

Technical

Documents

Tools &

Software

Support &Community

An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,intellectual property matters and other important disclaimers. PRODUCTION DATA.

PGA280SBOS487B –JUNE 2009–REVISED MARCH 2020

PGA280 Zerø-Drift, High-Voltage,Programmable Gain Instrumentation Amplifier

1

1 Features1• Wide input range: ±15.5 V at ±18-V supply• Binary gain steps: 128V/V to 1/8 V/V• Additional scaling factor: 1 V/V and 1⅜ V/V• Low offset voltage: 3 μV at G = 128• Near-zero long-term drift of offset voltage• Near-zero gain drift: 0.5 ppm/°C• Excellent linearity: 1.5 ppm• Excellent CMRR: 140 dB• High input impedance• Very low 1/f noise• Differential signal output• Overload detection• Input configuration switch matrix• Wire break test current• Expandable SPI™ with checksum• General-purpose I/O port• TSSOP-24 package

2 Applications• Analog input module• Data acquisition (DAQ)• Aircraft engine control• Battery test

3 DescriptionThe PGA280 is a high-precision instrumentationamplifier with digitally-controllable gain and signalintegrity test capability. This device offers low offsetvoltage, near-zero offset and gain drift, excellentlinearity, and nearly no 1/f noise with superiorcommon-mode and supply rejection to support high-resolution precision measurement. The 36-V supplycapability and wide, high-impedance input rangecomply with requirements for universal signalmeasurement.

Special circuitry prevents inrush currents frommultiplexer (MUX) switching. In addition, the inputswitch matrix enables easy reconfiguration andsystem-level diagnostics—overload conditions areindicated.

The configurable general-purpose input/output(GPIO) offers several control and communicationfeatures. The SPI can be expanded to communicatewith more devices, supporting isolation with only fourISO couplers. The PGA280 is available in a TSSOP-24 package and is specified from –40°C to +105°C.For all available packages, see the package optionaddendum at the end of the data sheet.

Device ComparisonFEATURES PRODUCT

23-bit resolution, ΔΣ analog-to-digital converter ADS1259Chopper-stabilized instrumentation amplifier,RR I/O, 5V single-supply INA333

High-precision PGA, G = 1, 10, 100, 1000 PGA204High-precision PGA, JFET Input, G = 1, 2, 4, 8 PGA206

Typical Application

http://www.ti.com/product/pga280?qgpn=pga280http://www.ti.com/product/PGA280?dcmp=dsproject&hqs=pfhttp://www.ti.com/product/PGA280?dcmp=dsproject&hqs=sandbuysamplebuyhttp://www.ti.com/product/PGA280?dcmp=dsproject&hqs=tddoctype2http://www.ti.com/product/PGA280?dcmp=dsproject&hqs=swdesKithttp://www.ti.com/product/PGA280?dcmp=dsproject&hqs=supportcommunityhttp://www.ti.com/solution/analog-input-modulehttp://www.ti.com/solution/data-acquisition-daqhttp://www.ti.com/solution/aircraft-engine-controlhttp://www.ti.com/solution/battery-testhttp://focus.ti.com/docs/prod/folders/print/ads1259.htmlhttp://focus.ti.com/docs/prod/folders/print/ina333.htmlhttp://focus.ti.com/docs/prod/folders/print/pga204.htmlhttp://focus.ti.com/docs/prod/folders/print/pga206.html

2

PGA280SBOS487B –JUNE 2009–REVISED MARCH 2020 www.ti.com

Product Folder Links: PGA280

Submit Documentation Feedback Copyright © 2009–2020, Texas Instruments Incorporated

Table of Contents1 Features .................................................................. 12 Applications ........................................................... 13 Description ............................................................. 14 Revision History..................................................... 25 Pin Configuration and Functions ......................... 36 Specifications......................................................... 4

6.1 Absolute Maximum Ratings .................................... 46.2 Electrical Characteristics........................................... 46.3 Timing Requirements: Serial Interface...................... 76.4 Typical Characteristics .............................................. 8

7 Detailed Description ............................................ 157.1 Overview ................................................................. 157.2 Functional Block Diagram ....................................... 157.3 Feature Description................................................. 16

7.4 Device Functional Modes........................................ 247.5 Programming........................................................... 267.6 Register Map........................................................... 31

8 Application and Implementation ........................ 388.1 Application Information............................................ 38

9 Power Supply Recommendations ...................... 3910 Device and Documentation Support ................. 41

10.1 Receiving Notification of Documentation Updates 4110.2 Support Resources ............................................... 4110.3 Trademarks ........................................................... 4110.4 Electrostatic Discharge Caution............................ 4110.5 Glossary ................................................................ 41

11 Mechanical, Packaging, and OrderableInformation ........................................................... 41

4 Revision HistoryNOTE: Page numbers for previous revisions may differ from page numbers in the current version.

Changes from Revision A (September 2009) to Revision B Page

• Added Timing Characteristics: Serial Interface table and serial timing diagram.................................................................... 7• Changed text from "This interface allows.clock rates up to 10 Mhz." to "... 16 MHz" in last paragraph of SPI and

Register Description section ................................................................................................................................................ 26

http://www.ti.com/product/pga280?qgpn=pga280http://www.ti.comhttp://www.ti.com/product/pga280?qgpn=pga280http://www.ti.com/feedbackform/techdocfeedback?litnum=SBOS487B&partnum=PGA280

SCLK

SDI

SDO

DVDD

GPIO0

GPIO1

GPIO2

GPIO3

GPIO4

GPIO5

GPIO6

CS

INP1

INN1

VSN

DGND

VON

VOP

VOCM

VSOP

VSON

VSP

INP2

INN2

PGA280

16

15

14

13

24

23

22

21

20

19

18

17

9

10

11

12

1

2

3

4

5

6

7

8

3

PGA280www.ti.com SBOS487B –JUNE 2009–REVISED MARCH 2020


Submit Documentation FeedbackCopyright © 2009–2020, Texas Instruments Incorporated

5 Pin Configuration and Functions

TSSOP-24PW PACKAGE

(TOP VIEW)

Pin FunctionsPIN

DESCRIPTIONPIN

DESCRIPTIONNO. NAME NO. NAME1 VON Inverting signal output 13 DVDD Digital supply2 VOP Noninverting signal output 14 SDO SPI slave data output3 VOCM Input, output common-mode voltage 15 SDI SPI slave data input4 VSOP Positive supply for output 16 SCLK SPI clock input5 VSON Negative supply for output, AGND 17 CS SPI chip select input; active low6 VSP Positive high-voltage supply 18 GPIO6 GPIO 6, SYNC (in), OSC (out), ECS67 INP2 AUX input, noninverting 19 GPIO5 GPIO 5, BUFA (out), ECS58 INN2 AUX input, inverting 20 GPIO4 GPIO 4, BUFT (in), ECS49 INP1 Signal input, noninverting 21 GPIO3 GPIO 3, EF (out), ECS310 INN1 Signal input, inverting 22 GPIO2 GPIO 2, ECS2, MUX211 VSN Negative high-voltage supply 23 GPIO1 GPIO 1, ECS1, MUX112 DGND Digital ground 24 GPIO0 GPIO 0, ECS0, MUX0


4




(1) Stresses above these ratings may cause permanent damage. Exposure to absolute maximum conditions for extended periods maydegrade device reliability. These are stress ratings only, and functional operation of the device at these or any other conditions beyondthose specified is not implied.

(2) Terminals are diode-clamped to the power-supply (VON and VOP) rails. Signals that can swing more than 0.5V beyond the supply railsmust be current-limited.

(3) Short-circuit to VSON or VSOP, respectively, DGND or DVDD.

6 Specifications

6.1 Absolute Maximum Ratings (1)Over operating free-air temperature range, unless otherwise noted.

VALUE UNIT

Supply voltageVSN to VSP 40 VVSON to VSOP, and DGND to DVDD 6 V

Signal input terminals, voltage (2) VSN – 0.5 to VSP + 0.5 VSignal input terminals, current (2) ±10 mAOutput short-circuit (3) ContinuousOperating temperature –55 to +140 °CStorage temperature –65 to +150 °CJunction temperature +150 °CESD ratings Human body model (HBM) 2000 V

(1) RTI: Referred to input.(2) Specified by design; not production tested.(3) See Application Information section and typical characteristic graphs.(4) 300-hour life test at +150°C demonstrated randomly distributed variation in the range of measurement limits.

6.2 Electrical Characteristicsat TA = 25°C, VSP = 15 V, VSN = –15 V, VSON = 0 V, VSOP = 5 V, DVDD = 3 V, DGND = 0 V, RL = 2.5 kΩ to VSOP/2 =VOCM, G = 1 V/V, using internal clock, BUF inactive, VCM = 0 V, and differential input and output (unless otherwise noted)

PARAMETER TEST CONDITIONS MIN TYP MAX UNIT

INPUT

VOS Offset voltage, RTI (1)Gain = 1 V/V, 1.375 V/V ±50 ±250

µVGain = 128 V/V ±3 ±15

dVOS/dT vs temperature (2) TA = –40°C to +105°CGain = 1 V/V ±0.2 ±0.6

μV/°CGain = 128 V/V ±0.03 ±0.17

PSR vs power supply, RTI VSP – VSN = 10 V and 36 V,gain = 1 V/V, 128 V/V ±0.3 ±3 µV/V

dVOS/df vs external clock, RTI (3)0.8 MHz to 1.2 MHz, gain = 1 V/V ±0.05

μV/kHz0.8 MHz to 1.2 MHz, gain = 128 V/V ±0.001

Long-term stability (4) Gain = 128 V/V 3.5 nV/month

Input impedance Single-ended and differential > 1 GΩ

Input capacitance, IN1 / IN2 Single-ended 12 / 8 pF

Input voltage Gain = 1 V/V, gain = 128 V/V, TA = –40°C to +105°C (VSN) + 2.5 (VSP) – 2.5 V

CMR Common-mode rejection, RTI

Gain = 1 V/V ±0.3 ±3

μV/VGain = 128 V/V ±0.08 ±0.8

Gain = 128 V/V, TA = –40°C to +105°C ±0.1 ±1.5

SINGLE-ENDED OUTPUT CONNECTION

VOS Offset voltage, RTI, SE outGain = 1 V/V, 1.375 V/V, SE ±120

μVGain = 1V/V ±3

dVOS/dT vs temperature, SE outGain = 1 V/V, SE, TA = –40°C to +105°C 0.6

μV/°CGain = 64 V/V, SE, TA = –40°C to +105°C 0.05


5




Electrical Characteristics (continued)at TA = 25°C, VSP = 15 V, VSN = –15 V, VSON = 0 V, VSOP = 5 V, DVDD = 3 V, DGND = 0 V, RL = 2.5 kΩ to VSOP/2 =VOCM, G = 1 V/V, using internal clock, BUF inactive, VCM = 0 V, and differential input and output (unless otherwise noted)


(5) Gains smaller than ½ are measured with smaller output swing.(6) See Figure 11 for typical gain error drift of various gain settings.(7) Only G = 1 is production tested.

INPUT BIAS CURRENT (3)

IB Bias current

Gain = 1 V/V ±0.3 ±1

nAGain = 128 V/V ±0.8 ±2

Gain = 1 V/V, gain = 128 V/V, TA = –40°C to +105°C ±0.6 ±2

IOS Offset currentGain = 1 V/V, gain = 128 V/V ±0.1 ±0.5

nAGain = 1 V/V, gain = 128 V/V, TA = –40°C to +105°C ±0.9 ±2

NOISE

eNI Voltage noise, RTI; target

f = 0.01 Hz to 10 HzRS = 0 Ω, G = 128 V/V 420 nVPPRS = 0 Ω, G = 1 V/V 4.5 μVPP

f = 1 kHzRS = 0 Ω, G = 128 V/V 22 nV/√Hz

RS = 0 Ω, G = 1 V/V 240 nV/√Hz

IN Current noise, RTIf = 0.01 Hz to 10 Hz RS = 10 MΩ, G = 128 V/V 1.7 pAPPf = 1 kHz RS = 10 MΩ, G = 128 V/V 90 fA/√Hz

GAIN (Output Swing = ±4.5 V) (5)

Range of input gain ⅛ to 128 V/V

Range of output gain 1 and 1⅜ V/V

Gain error, all binary steps All gains ±0.03 ±0.15 %

vs temperature (2) (6)No load, all gains except G = 128 V/V, TA = –40°C to+105°C –0.5 ±2 ppm/°C

No load, G = 128 V/V, TA = –40°C to +105°C –1 ±3 ppm/°C

Gain step matching (3) (gain togain) No load, all gains See Typical Characteristics

Nonlinearity No load, all gains (7) 1.5 10 ppm

Nonlinearity overtemperature (2) No load, all gains, TA = –40°C to +105°C 3 ppm

OUTPUT

Voltage output swing fromrail (3) TA = –40°C to +105°C

VSOP = 5 V,load current 2 mA 40 100 mV

VSOP = 2.7 V,load current 1.5 mA 100 mV

Capacitive load drive 500 pF

ISC Short-circuit current To VSOP/2, gain = 1.375 V/V 7 15 25 mA

Output resistance Each output VOP and VON 200 mΩ

VOCM

VOCM supply voltage VSP – 2 V > VOCM, TA = –40°C to +105°C(VSON) +

0.1(VSOP) –

0.1 V

IB Bias current into VOCM 3 100 nA

VOCM input resistance 1 GΩ

INTERNAL OSCILLATOR

Frequency of internalclock (2) (3) 0.8 1 1.2 MHz

Ext. oscillator frequency 0.8 1 1.2 MHz


6




Electrical Characteristics (continued)at TA = 25°C, VSP = 15 V, VSN = –15 V, VSON = 0 V, VSOP = 5 V, DVDD = 3 V, DGND = 0 V, RL = 2.5 kΩ to VSOP/2 =VOCM, G = 1 V/V, using internal clock, BUF inactive, VCM = 0 V, and differential input and output (unless otherwise noted)


FREQUENCY RESPONSE

GBP Gain bandwidth product (3) G > 4 6 MHz

SR Slew rate (3), 4-VPP output step

G = 1, CL = 100 pF, BUF On 1 V/μs

G = 8, CL = 100 pF 2 V/μs

G = 128, CL = 100 pF 1 V/μs

tS Settling time (3)To 0.01%

G = 8, VO = 8-VPP step 20 μs


To 0.001%G = 8, VO = 8-VPP step 30 μs


Overload recovery, input (3) 0.5 V over supply, G = ⅛ to 128 8 μs

Overload recovery, output (3) ±5.5-VP input, G = 1 V/V 6 μs

INPUT MULTIPLEXER (Two-Channel)

Crosstalk, INP1 to INP2 At dc, gain = 128 V/V < –130 dB

Series-resistance (3)—seeFigure 44 600 Ω

Switch on-resistance (3) 450 Ω

Current source and sink (3) To GND 70 95 125 μA

INPUT CURRENT BUFFER (BUF)

VOS Offset voltage (3) Buffer active 15 mV

DIGITAL I/O (Supply: 2.7 V to 5.5 V)

Input (logic low threshold) 0 (DVDD)x0.2 V

Input (logic high threshold) 0.8x(DVDD) DVDD V

Output (logic low) IOUT = 4 mA, sink 0.7 V

Output (logic high) IOUT = 2 mA, source DVDD – 0.5 V

SCLK, frequency 10 MHz

POWER SUPPLY: Input Stage (VSN – VSP)

Specified voltage TA = –40°C to +105°C 10 36 V

Operating voltage 10 to 38 V

IQ Quiescent current TA = –40°C to +105°CVSP 2.4 3 mA

VSN 2.1 3 mA

POWER SUPPLY: Output Stage (VSOP – VSON)

Specified voltage VSP – 1.5 V ≥ VSOP, TA = –40°C to +105°C 2.7 5.5 V

Voltage for VSOP, upper limit (VSP – 2 V) > VOCM, (VSP – 5 V) > VSON (VSP) V

Voltage for VSON (VSP – 2 V) > VOCM, VSP ≥ VSOP (VSN) to(VSP) – 5 V

IQ Quiescent Current VSOP, TA = –40°C to +105°C 0.75 1 mA

POWER SUPPLY: Digital (DVDD – DGND)

Specified voltage TA = –40°C to +105°C 2.7 5.5 V

Voltage for DVDD, upper limit (VSP) – 1 V

Voltage for DGND, lower limit (VSN) V

IQ Quiescent current (3)Static condition, no external load,DVDD = 3 V, TA = –40°C to +105°C

0.07 0.13 mA

TEMPERATURE

Specified temperature –40 105 °C

Operating temperature –55 140 °C

θJA Thermal resistance SSOP, High-K board, JESD51 80 °C/W


SCLK

CS

tSU_CSCK tHT_CKCS

tDZ_CSDO

SCLK

SDI

SDO

tCLK

tSU_CKDI

tHT_CKDI

tD_CKDO

7




6.3 Timing Requirements: Serial Interfaceat TA = –40°C to +105°C, DVDD = 2.7 V to 5.5 V, and CLOAD on SDO = 20 pF (unless otherwise specified)

MIN NOM MAX UNITfSCLK Serial clock frequency 16 MHztCLK Serial clock time period 62.5 nstSU_CSCK Setup time: CS falling to first SCLK capture (falling) edge 0 nstHT_CKCS Delay time: last SCK capture (falling) to CS rising 0 nstSU_CKDI Setup time: SDI data valid to SCLK capture (falling) edge 5 nstHT_CKDI Hold time: SCLK capture (falling) edge to previous data valid on SDI 10 nstDZ_CSDO Delay time: CS rising to SDO going to Hi-Z 25 nstD_CKDO Delay time: SCLK rising edge to (next) data valid on SDO 25 ns

Figure 1. Serial Timing Diagram


-3.0

-2.7

-2.4

-2.1

-1.8

-1.5

-1.2

-0.9

-0.6

-0.3 0

0.3

0.6

0.9

1.2

1.5

1.8

2.1

2.4

2.7

3.0

Common-Mode Rejection Ratio ( V/ )m V

120

100

80

60

40

20

0

Popula

tion (

%)

-3.0

-2.7

-2.4

-2.1

-1.8

-1.5

-1.2

-0.9

-0.6

-0.3 0

0.3

0.6

0.9

1.2

1.5

1.8

2.1

2.4

2.7

3.0

Common-Mode Rejection Ratio ( V/ )m V

80

70

60

50

40

30

20

10

0

Popula

tion (

%)

-0

.20

-0

.18

-0

.16

-0

.14

-0

.12

-0

.10

-0

.08

-0

.06

-0

.04

-0

.02 0

0.0

2

0.0

4

0.0

6

0.1

0

0.1

2

0.1

4

0.1

6

0.1

8

0.2

0

Offset Voltage Drift ( V/ C)m °

50

45

40

35

30

25

20

15

10

5

0

Po

pu

latio

n (

%)

-1.0

-0.9

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Offset Voltage Drift ( V/ C)m °

50

45

40

35

30

25

20

15

10

5

0

Popula

tion (

%)

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2 0 2 4 6 8

10

12

14

16

18

20

Offset Voltage ( V)m

50

45

40

35

30

25

20

15

10

5

0

Popula

tion (

%)

-3

00

-2

70

-2

40

-2

10

-1

80

-1

50

-1

20

-9

0

-6

0

-3

0 0

30

60

90

12

0

15

0

18

0

21

0

24

0

27

0

30

0

Offset Voltage ( V)m

50

45

40

35

30

25

20

15

10

5

0

Po

pu

latio

n (

%)

8




6.4 Typical CharacteristicsAt TA = +25°C, VSP = +15V, VSN = –15V, VSON = 0V, VSOP = 5V, DVDD = +3V, DGND = 0V, RL = 2.5kΩ to VSOP/2 =VOCM, G = 1V/V, using internal clock, BUF inactive, VCM = 0V, and differential input and output, unless otherwise noted.

Figure 2. Offset Voltage Production Distribution (G = 128) Figure 3. Offset Voltage Production Distribution (G = 1)

Figure 4. Offset Voltage Drift Distribution (G = 128) Figure 5. Offset Voltage Drift Distribution (G = 1)

Figure 6. Common-Mode Rejection Distribution (G = 128) Figure 7. Common-Mode Rejection Distribution (G = 1)


0.20

0.15

0.10

0.05

0

0.05

0.10

0.15

0.20

-

-

-

-

Ga

in E

rro

r: M

ea

n3

(%)

s±

1/8

to

1/4

1/4

to

1/2

1/2

to

1

1 t

o 1 t

o 2

2 t

o 4

4 t

o 8

8 t

o 1

6

16

to

32

32

to

64

64

to

12

8

Gain Setting Change

38

1

0.20

0.15

0.10

0.05

0

0.05

0.10

0.15

0.20

-

-

-

-

Gain

Err

or:

Mean

3(%

)s

±

1/8

1/4

1/2 1 2 4 8 16

32

64

128

Gain Setting (V/V)

38

1

3

2

1

0

1

2

3

-

-

-

Gain

Err

or

Drift: M

ean

3(p

pm

/C

)s

±°

1/8

1/4

1/2 1 2 4 8 16

32

64

128

Gain Setting (V/V)

38

11/8 1/4 1/2 1 2 4 8 16 32 64 1283 81

Gain Setting (V/V)

0.15

0.10

0.05

0

0.05

0.10

0.15

-

-

-

Ga

in E

rro

r (%

)

Selected samples with typical performance

-0

.20

-0

.18

-0

.16

-0

.14

-0

.12

-0

.10

-0

.08

-0

.06

-0

.04

-0

.02 0

0.0

2

0.0

4

0.0

6

0.0

8

0.1

0

0.1

2

0.1

4

0.1

6

0.1

8

0.2

0Gain Error (%)

70

60

50

40

30

20

10

0

Po

pu

latio

n (

%)

-0

.20

-0

.18

-0

.16

-0

.14

-0

.12

-0

.10

-0

.08

-0

.06

-0

.04

-0

.02 0

0.0

2

0.0

4

0.0

6

0.0

8

0.1

0

0.1

2

0.1

4

0.1

6

0.1

8

0.2

0

Gain Error (%)

30

25

20

15

10

5

0

Po

pu

latio

n (

%)

9




Typical Characteristics (continued)At TA = +25°C, VSP = +15V, VSN = –15V, VSON = 0V, VSOP = 5V, DVDD = +3V, DGND = 0V, RL = 2.5kΩ to VSOP/2 =VOCM, G = 1V/V, using internal clock, BUF inactive, VCM = 0V, and differential input and output, unless otherwise noted.

Figure 8. Gain-Error Distribution (G = 128) Figure 9. Gain-Error Distribution (G = 1)

Figure 10. Gain Error vs Gain Setting Figure 11. Gain-Error Drift Distributionvs Gain Setting (Mean With ±3 σ)

Figure 12. Maximum Gain-Error Deviation BetweenSequential Gain Settings (Mean With ±3 σ)

Figure 13. Gain-Error Distribution vsGain Setting (Mean With ±3σ)


3.0

2.5

2.0

1.5

1.0

0.5

0

Inp

ut

Vo

lta

ge

Sw

ing

to

Ra

il (V

)

-50 -25 0 50 100 150

Temperature ( C)°

IR-

IR+

25 75 125

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0

Inp

ut

Bia

s C

urr

en

t (n

A)

1 2 4 8 16 32 64 128

Gain Setting (V/V)

100

10

1

0.1

0.01

No

ise

(V

/)

mH

zÖ

0.1 1 10 100 1k 10k 100k

Frequency (Hz)

G = 1/8

G = 1

G = 4

G = 128

60

50

40

30

20

10

0

10

20

-

-

Ga

in (

dB

)

10 100 1k 10k 100k 1M 10M

Frequency (Hz)

140

120

100

80

60

40

20

0

Po

we

r-S

up

ply

Re

jectio

n R

atio

(d

B)

10 100 1k 10k 100k

Frequency (Hz)

VSN

VSP

140

120

100

80

60

40

20

0

Co

mm

on

-Mo

de

Re

jectio

n R

atio

(d

B)

10 100 1k 10k 100k

Frequency (Hz)

10





Figure 14. Power-Supply Rejection vs Frequency Figure 15. Common-Mode Rejection vs Frequency

Figure 16. Input-Referred Noise Spectrum Figure 17. Small-Signal Gain vs Frequency

Figure 18. Input Voltage Range Limits vs Temperature Figure 19. Bias Current vs Gain Setting


3.0

2.5

2.0

1.5

1.0

0.5

0

Quie

scent C

urr

ent (m

A)

I VSPQ

I VSOPQ

-50 -25 0 50 100 150

Temperature ( C)°

25 75 125 -50 -25 0 50 100 150

Temperature ( C)°

25 75 125

90

85

80

75

70

65

60

1.0

0.9

0.8

0.7

0.6

0.5

0.4

Dig

ita

l S

up

ply

Cu

rre

nt,

no

SP

I (

A)

m

Dig

ital S

upp

ly C

urre

nt, w

ith S

PI (m

A)

I (no SPI)DVDD

I (with SPI)DVDD

-1.0

-0.9

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Input Offset Current (nA)

70

60

50

40

30

20

10

0

Popula

tion (

%)

10

8

6

4

2

0

2

4

6

8

10

-

-

-

-

-

I/I

Cu

rre

nt

(nA

)B

IAS

OS

-50 -25 0 50 100 150

Temperature ( C)°

IN1_I _1

IN1_I _128

IN1_ _1

IN1_I _128

BIAS

BIAS

OFFSET

IOFFSET

25 75 125

IOFFSET

IBIAS

-1.0

-0.9

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Bias Current (nA)

80

70

60

50

40

30

20

10

0

Popula

tion (

%)

-1.0

-0.9

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Bias Current (nA)

90

80

70

60

50

40

30

20

10

0

Popula

tion (

%)

11





Figure 20. Input Bias Current Distribution (G = 128) Figure 21. Input Bias Current Distribution (G = 1)

Figure 22. Input Offset Current Distribution (G = 1, G = 128) Figure 23. Input Bias Current and Input Offset Currentvs Temperature

Figure 24. Quiescent Current From Supplies (VSP andVSOP) vs Temperature

Figure 25. Digital Supply CurrentWith and Without SPI Communication

vs Temperature


20

19

18

17

16

15

14

13

12

11

10

Curr

ent Lim

it (

mA

)

Positive

Negative

-50 -25 0 50 100 150

Temperature ( C)°

25 75 125

100

90

80

70

60

50

40

30

20

10

0

Outp

ut S

win

g to R

ail

(mV

)

-50 -25 0 50 100 150

Temperature ( C)°

25 75 125

Positive Rail

Negative Rail

8.0

8.8

9.6

10.4

11.2

12.0

12.8

13.6

14.4

15.2

16.0

16.8

17.6

18.4

19.2

20.0

20.8

21.6

22.4

23.2

24.0

Positive Current Limit (mA)

16

14

12

10

8

6

4

2

0

Popula

tion (

%)

8.0

8.8

9.6

10.4

11.2

12.0

12.8

13.6

14.4

15.2

16.0

16.8

17.6

18.4

19.2

20.0

20.8

21.6

22.4

23.2

24.0

Negative Current Limit (mA)

14

12

10

8

6

4

2

0

Popula

tion (

%)

0

1

2

3

4

5

6

7

8

9

10

-

-

-

-

-

-

-

-

-

-

No

nlin

ea

rity

(p

pm

)

-4 -3 -2 -1 0 1 2 3 4

Input/Output Voltage (V)

Selected samples with typical performance

10

9

8

7

6

5

4

3

2

1

0

No

nlin

ea

rity

(p

pm

)

-50 -25 0 50 100 150

Temperature ( C)°

25 75 125

12





Figure 26. Gain Nonlinearity With End-Point Calibration(G = 1)

Figure 27. Gain Nonlinearity vs Temperature

Figure 28. Positive Output Current Limit Distribution Figure 29. Negative Output Current Limit Distribution

Figure 30. Output Current Limit vs Temperature Figure 31. Output Swing To Rail vs Temperature(VSOP – VSON = 5 V)


-0.2

0

-0.1

8

-0.1

6

-0.1

4

-0.1

2

-0.1

0

-0.0

8

-0.0

6

-0.0

4

-0.0

2 0

0.0

2

0.0

4

0.0

6

0.0

8

0.1

0

0.1

2

0.1

4

0.1

6

0.1

8

0.2

0

D mV ( V/kHz)OS

80

70

60

50

40

30

20

10

0

Popula

tion (

%)

-0.2

0

-0.1

8

-0.1

6

-0.1

4

-0.1

2

-0.1

0

-0.0

8

-0.0

6

-0.0

4

-0.0

2 0

0.0

2

0.0

4

0.0

6

0.0

8

0.1

0

0.1

2

0.1

4

0.1

6

0.1

8

0.2

0

D mV ( V/kHz)OS

25

20

15

10

5

0

Popula

tion (

%)

75.0

77.5

80.0

82.5

85.0

87.5

90.0

92.5

95.0

97.5

100.0

102.5

105.0

107.5

110.0

112.5

115.0

117.5

120.0

122.5

125.0

Wire Break Current ( A)m

45

40

35

30

25

20

15

10

5

0

Popula

tion (

%)

Wire Break +

Wire Break -

-50 -25 0 50 100 150

Temperature ( C)°

25 75 125

100

98

96

94

92

90

88

86

84

82

80

Wire B

reak C

urr

ent (

A)

m

Wire Break Negative

Wire Break Positive

-20 -15 -10 -5 0 5 10 15 20

Common-Mode Voltage (V)

1600

1400

1200

1000

800

600

400

200

0

Re

sis

tan

ce

()

W Series Input

Resistance

Switch On

at V = 18VS ±

Switch On

at V = 15VS ±

Switch On

at V = 10VS ±Switch On

at V = 5VS ±

800

700

600

500

400

300

200

100

0

Re

sis

tan

ce

()

W Switch On

V = 15VS ±

Series In R

-50 -25 0 50 100 150

Temperature ( C)°

25 75 125

13





Figure 32. Switch-On Resistanceand Series Input Resistance

vs Common-Mode Voltage at Various Supply Voltages

Figure 33. Switch-On Resistanceand Series Input Resistance

vs Temperature

Figure 34. Wire Break Current Distribution Figure 35. Wire Break Current Magnitude vs Temperature

Figure 36. Influence of External Clock Frequency toVOS Performance (G = 128)

Figure 37. Influence of External Clock Frequency toVOS Performance (G = 1)


-100

-90

-80

-70

-60

-50

-40

-30

-2

0

-10 0

10

20

30

40

50

60

70

80

90

100

Buffer Offset Voltage (mV)

30

25

20

15

10

5

0

Popula

tion (

%)

1.20

1.15

1.19

1.05

1.00

0.95

0.90

0.85

0.80

Oscill

ato

r F

req

ue

ncy (

MH

z)

-50 -25 0 50 100 150

Temperature ( C)°

25 75 125

10 s/divm

5V

/div

5V

/div

2V

/div

Diff Signal Output

(Right Scale)

INN1

(INP1 to GND)

(Left Scale)

Error Flag (Not Latched)

10 s/divm

VOP (1V/div)

VON (1V/div)

INN1 (5V/div)

EF_OUTERR

VSON (GND)

G = 1, VSOP (5V)

10 s/divm

5V

/div

50

mV

/div 2

V/d

iv

Diff Signal

Output

(Right Scale)

INN1

(Left Scale)

Error Flag

10 s/divm

2V

/div

50

0m

V/d

iv 2V

/div

Diff Signal

Output

(Right Scale)

INN1 Single-Ended

(INP1 to GND)

(Left Scale)Error Flag

14





Figure 38. Step Response (G = 128) Figure 39. Step Response (G = 8)

Figure 40. Step Response (G = 1) Figure 41. Output Overload Recovery

Figure 42. Oscillator Frequency vsTemperature

Figure 43. Input Current Buffer Offset Voltage Distribution


Gain

MUX

Switch Network,

Current Source

and Sink,

and Buffer

Digital I/O

VSPVSN

VSOP

VSON

Control Registers

DGND DVDD

INP1

INN1

INP2

INN2

SPI

7x GPIO

VOP

VOCM

VON

15




7 Detailed Description

7.1 OverviewThe PGA280 is a universal high-voltage instrumentation amplifier with digital gain control. This device offersexcellent dc precision and long-term stability using modern chopper technology with internal filters that minimizechopper-related noise. The input gain extends from ⅛ V/V (attenuation) to 128 V/V in binary steps. The outputstage offers a gain multiplying factor of 1 V/V and 1⅜ V/V for optimal gain adjustment. The output stage connectsto the low-voltage (5 V or 3 V) supply. .

A signal multiplexer provides two differential inputs. Several signal switches allow signal diagnosis of wire break,input disconnect, single-ended (versus differential), and shorted inputs.

The supply voltage of up to ±18 V offers a wide common-mode range with high input impedance; therefore, largecommon-mode noise signals and offsets can be suppressed.

A pair of high-speed current buffers can be activated to avoid inrush currents during fast signal transients, suchas those generated from switching the signal multiplexers. This feature minimizes discharge errors in passivesignal input filters in front of the multiplexer.

The fully differential signal output matches the inputs of modern high-resolution and high-accuracy analog-to-digital converters (ADCs), including delta-sigma (ΔΣ) as well as successive-approximation response (SAR)converters. The supply voltage for the output stage is normally connected together with the converter supply,thus preventing signal overloads from the high-voltage analog supply.

Internal error detection in the input and output stage provides individual information about the signal condition.Integrating ADCs may hide momentary overloads. Together with the input switch matrix, extensive signal anderror diagnosis is made possible.

The serial peripheral interface (SPI) provides write and read access to internal registers. These registers controlgain, the current buffer, input switches, and the general-purpose input/output (GPIO) or special function pins, aswell as configuration and diagnostics.

The GPIO port controls the multiplexer (MUX) and switches and indicates internal conditions. The GPIO port canalso be individually configured for output or input. A special CS mode for the GPIO extends the communication toother external SPI devices, such as data converters or shift registers. This special function is intended for SPIcommunication via a minimum number of isolation couplers. Additional proof for communication integrity isprovided by an optional checksum byte following each communication block.

7.2 Functional Block Diagram


16




7.3 Feature Description

7.3.1 Functional BlocksBoth high-impedance input amplifiers are symmetrical, and have low noise and excellent dc precision. Theseamplifiers are connected to a resistor network and provide a gain range from 128 V/V down to an attenuation of⅛. The PGA280 architecture rejects common-mode offsets and noise over a wide bandwidth.

The PGA280 features additional current buffers placed in front of the precision amplifier that can be activated ondemand. When activated, these additional current buffers avoid problems that result from input current duringdynamic overloads, such as the fast signal transient that follows the channel switching from a multiplexer.Without the use of the additional current buffers, the fast signal transient would overload the precision amplifiersand high bias currents could flow into the protection clamp until the amplifiers recover from the overload. Thismomentary current can influence the signal source or passive filters in front of the multiplexer and generate longsettling tails. Activating this current buffer avoids such an overload current pulse. The buffer disconnectsautomatically after an adjustable time. For continuous signal measurement, the additional current buffers are notused.

The switches in the input provide signal diagnostic capability and offer an auxiliary input channel (INP2 andINN2; see Figure 44). Both channels can be switched to diagnose or test conditions, such as a ground-referred,single-ended voltage measurement for either input. In this mode, each of the signal inputs can be observed toanalyze common-mode offsets and noise.

The primary input channel [INP1 and INN1] provides switches and current sources for a wire break test. Anyswitch can short both inputs, and can also discharge a filter capacitor after a wire break test, for example.

The signal inputs are diode-clamped to the supply rails. External resistors can be placed in series to the inputs toprovide overvoltage protection. Limit current into the input pins to ≤ 10 mA.

The output stage offers a fully-differential signal around the output reference pin, VOCM. The VOCM pin is ahigh-impedance input and expects an external voltage, typically close to midsupply. The 3-V or 5-V supply of theconverter or amplifier, following the PGA280 outputs, is normally connected to VSOP and VSON; thisconfiguration shares a common supply voltage and protects the circuit from overloads. The fully-differential signalavoids coupling of noise and errors from the supply and ground, and allows large signal swing without the risk ofnonlinearities that arise when driving near the supply rails.

The PGA280 signal path has several test points for critical overload conditions. The input amplifiers detect signalovervoltage and overload as a result of high gain. The output stage also detects clipping. These events arefiltered with adjustable suppression delays and then stored for readout. A GPIO pin can be dedicated for externalindication either as an interrupt or in a monitor mode.

A serial peripheral interface (SPI) controls the gain setting and switches, as well as the operation modes and theGPIO port pins. The SPI allows read and write access to the internal registers. These registers containconditions, flags, and settings, as described in the SPI and Register Description section. They represent the gainsetting for the input stage from 128V/V to the attenuation of ⅛ V/V in binary steps and the output stage gain of 1V/V and 1.375 V/V (1⅜). The input MUX and switches and the input buffers are also controlled by registers.Internal error conditions are stored and may be masked to activate an external pin in the GPIO port.

This GPIO port can be configured individually for either input or output or for a special function. In specialfunction mode, the port indicates an error condition, generates CS signal, controls an external MUX, andconnects to the buffer control and oscillator.

The port pin can act as a CS for an external SPI device. This mode connects other SPI devices [such as ananalog-to-digital (A/D) converter] to the primary four-wire SPI. This feature is especially desirable when usinggalvanically-isolated SPI communication. An optional checksum byte further improves communications integrity.


600W

600W

VSP

VSON

VSON

100 A

Source

m

100 A

Sink

m

F1

F2

D12

G1

G2

C1

B1

A1b

B1b

A1

INP2

INP1

BUF

600W

600W

VSON

DVDD DGND

VSON

C2

B2

A2b

B2b

A2

INN2

INN1

BUF

VSN

Gain

Network

Serial Peripheral Interface

and Controls

17




Feature Description (continued)7.3.1.1 Input Switch NetworkFigure 44 shows the arrangement of the input switches. They are controlled individually via the digital SPI. Theswitches B1b, B2b, A1b, and A2b are controlled automatically with the buffer (BUF) operation.

Figure 44. Input Switch Diagram

Switches A and B select the signal input. Input 1 (INP1 and INN1) provides two current sources and two switchesthat connect to VSON (which is typically the analog ground). This configuration is intended for wire breakdiagnosis. D12 can discharge an external capacitor or generate a starting condition.

Switches C1 and C2 are used to measure the input voltage referred to GND (VSON); for example, with A1 andC2 closed. This scheme measures the voltage signal connected to the input pin (INP1) referred to a commonground. The BUF output is protected against a short to VSON. See the SPI and Register Description section formore information about switch control.


1 s/divm

Signal Input

to INP1

Ch 4, 2V/div

1.5k Connecting to INP1W

Ch 2, 2V/div

Diff Signal Output

Ch 1, 1V/div

18




Feature Description (continued)7.3.1.2 Input Amplifier, Gain Network, and BufferThe high-precision input amplifiers present very low dc error and drift as a result of a modern chopper technologywith an embedded synchronous filter that removes virtually all chopping noise. This topology reduces flickernoise to a minimum and therefore enables the precise measurement of small dc-signals with high resolution,accuracy, and repeatability. The chopper frequency of 250 kHz is derived from an internal 1-MHz clock. Anexternal clock can also be connected, if desired.

The gain network for the binary gain steps connects to the input amplifiers, thus providing the best possiblesignal-to-noise ratio (SNR) and dc accuracy up to the highest gains. Gain is controlled by Register 0. Thisregister can control the gain and address for an external MUX in one byte. Selectable gains (in V/V) are : 128,64, 32, 16, 8, 4, 2, 1, ½, ¼, and ⅛. The gain is set to 1/8 V/V after device reset or power-on.

Programmable gain amplifiers such as the PGA280 use internal resistors to set the gain. Consequently,quiescent current is increased by the current that passes through these resistors. The largest amplitude couldincrease the supply current by ±0.4 mA. In maximum overload, gain of 128 V/V and each or the inputs connectedto the opposite supply voltage, a current of approximately 27 mA was measured. External resistors in series withthe input pins that are normally present avoid this extreme condition. This current is only limited by the internal600 Ω and the switch-on resistance (see Figure 44).

7.3.1.3 Current BufferDesigned for highest accuracy and low noise, both amplifier inputs are protected from dynamic overvoltagesthrough clamps. The amplifier fast input slew rate (approximately 1 V/µs) normally prevents these clamps fromturning on, provided adequate signal filtering is placed before the input. However, the fast channel switching-transient of a multiplexer or switch is much steeper, and cannot be filtered; this type of transient generates adynamic overload. The current buffers (BUF) prevent this dynamic overload condition of the input.

With the buffers not activated, Figure 45 indicates the clamp current flowing as a result of a fast signal change.The ramp in the signal, measured at the input pins (INP1), is the resulting voltage drop across the 1.5-kΩresistor. In the example measurement, this resistor is placed between the signal generator and the input pin ofthe PGA280.

Figure 45. Buffer OFF: Input Clamp Current Flowing


Instrumentation

AmplifierMux

Low-Pass

Filters

Ch x

Ch 3

Ch 2

Ch 1S1

S2

S3

Sx

Ideal

ActualChange of Mux

Output Voltage Ch 1

Ch 2

Current into

Protection Clamp

Long Settling of

Voltage on Ch 2

19




Feature Description (continued)Figure 46 shows a typical block diagram for multiplexed data acquisition. The transient from channel 1 to channel2 , shown as a voltage step, dynamically overloads the amplifier. A current pulse results from the input protectionclamp. Without the activation of the buffers (see BUF, Figure 44), the clamp current charges the filter and thesignal source. Input low-pass filters are often set to settling times in the millisecond range; therefore, dischargecurrents from dynamic overload would produce long settling delays.

NOTE: Current from the protection clamp into the signal source and filter produces a long settling delay.

Figure 46. Typical Block Diagram for Multiplexed Data Acquisition


100 s/divm

5V

/div

1V

/div

t2t1

Mux Switching

Inputs to PGA

with Buffer OFFInputs to PGA

with Buffer ON

Buffer Activated

20




Feature Description (continued)Together with the switching command of the multiplexer or internal switching, the current buffers (BUF) can beactivated to prevent such clamp currents. The buffers do not have clamps as long as the signal remains withinthe supply boundaries. Figure 47 shows an example of the input signal settling for both conditions: without andwith the buffer activated.

Without the buffer, there is an obvious long settling, depending on signal and filter impedance. With the bufferactivated, only the amplifier has to settle and no distorting current is reflected into the signal source and filter; noglitch is visible in this plot. The plot shows the resulting settling of the input signal for a positive and a negativesignal step as indicated in Figure 46; also shown are the SPI signal and the BUFA signal.

Figure 47. Example for Amplifier Settling Without (t1) and With (t2) Buffer (BUF) Activated

The buffers turn off automatically after a preset time (see Register 3, BUFTIM). They are activated from bit 5 (T)within the command byte. They can also be triggered by an external pin (BUFTin on GPIO4). The BUFA bit isactive in conjunction with the buffer, indicating that the buffer is busy (see Figure 55).

Error detection circuits observe the signal path for signal overvoltage (IOVerr), amplifier output clipping (IARerr),and gain overload (GAINerr). The Input Clamp Activation indicator ICAerr indicates that current was conductedinto the dynamic clamp circuit. These indicators help prevent misinterpretation of the analog signal and diagnosecritical input signal conditions, such as those that occur with integrating analog-to-digital converters that may hidemomentary overloads and present inaccurate results.

The buffers (BUF) prevent current flowing from the signal source with a compromise of offset voltage. As soon asthe buffers are turned off, the amplifiers settle back to high precision. For signal measurement without(multiplexer) switching transients, the buffer is not used.

7.3.1.4 Input ProtectionThe input terminals are protected with internal diodes connected to VSP and VSN. If the input signal voltageexceeds the power-supply voltage (VSP and VSN), limit the current to less than 10 mA to protect the internalclamp diodes. This current-limiting can generally be accomplished with a series input resistor.

7.3.1.5 EMI SusceptibilityAmplifiers vary in susceptibility to electromagnetic interference (EMI), but good layout practices play a criticalrole. EMI can generally be identified as a variation in offset voltage shifts. The PGA280 has been specificallydesigned to minimize susceptibility to EMI by incorporating an internal low-pass filter. Additional EMI filters maybe required next to the signal inputs of the system, as well as known good practices such as using short traces,low-pass filters, and damping resistors combined with parallel and shielded signal routing, depending on the endsystem requirements.


R

50

2

W

R

50

1

W

VOP

VON

R

100

4

W

R

100

3

W

VOP

VON

C

10 nF

1

C

10 nF

2C

10 nF

3

21




Feature Description (continued)7.3.1.6 Output StageThe output stage power is connected to the low-voltage supply (normally 3 V or 5 V) that is used by thesubsequent signal path of the system. This design prevents overloading of the low-voltage signal path.

The output signal is fully differential around a common-mode voltage (VOCM). The VOCM input pin is typicallyconnected to midsupply voltage to offer the widest signal amplitude range. VOCM is a high-impedance input thatrequires an external connection to a voltage within the supply boundaries. The usable voltage range for theVOCM input is specified in the Electrical Characteristics and must be observed.

The output stage can be set to a gain of 1 V/V and 1⅜ V/V. THe output stage is set to 1 V/V after a device resetor power-on, and is controlled by the gain multiplication factor.

Both signal outputs, VOP and VON, swing symmetrically around VOCM. The signal is represented as the voltagebetween the two outputs and does not require an accurate VOCM. Therefore, the signal output does not includeground noise or grounding errors. Noise or drift on VOCM is normally rejected by the common-mode rejectioncapability of the subsequent signal stage.

The signal that passes through the output stage is internally monitored for two error conditions: clipping of thesignal to the supply rail and overcurrent. In fault conditions, an error flag bit is set (OUTerr).

7.3.1.7 Output FilterThe PGA280 uses chopper technology for excellent dc stability over temperature and life of operation. Thedevice is designed to avoid 1/f frequency (flicker) noise, and therefore enables both high resolution and highrepeatability for dc measurements. While the chopper noise components are internally filtered, a minimal residualamount of high-frequency switching noise appears at the signal outputs. An external, passive, low-pass filter afterthe output stage is recommended to remove this switching noise; Figure 48 shows two examples. This filter canalso be used to isolate or decouple the charge switching pulses of an A/D converter input.

Figure 48. Typical Examples of Recommended Output Filters

7.3.1.8 Single-Ended OutputThe output stage of PGA280 is designed for highest precision. The fully-differential output avoids groundingerrors and noise, and delivers twice the signal amplitude compared to single-ended signals. However, if desired,the output can be taken single-ended from one of the output pins referred to the voltage at the VOCM pin. Theoutput stage errors now relate to half the signal amplitude and half the signal gain. The unused output isunconnected, but not disconnected from error detection. The usable voltage range for the VOCM input isspecified in the Electrical Characteristics and must be observed: the output swing (of both outputs) should notsaturate to the supply. Separate specifications for offset voltage and drift indicate higher offset voltage at lowergains, because some error sources are not cancelled in the output stage connected in single-ended mode. Notethat the gain is one-half of the gain set in reference to the gain table (see Table 2).


A3

A1

A2

Gain

Clamp

Clamp

MUX

Switch Network,

Current Source

and Sink,

and Buffer

Digital I/O

Error:

Input over-voltage Error:

Input amp saturationError:

Output amplifier

Error:

Gain network

overload

VSP VSOP

VSN VSON

VSP

VSN

VSP

VSNVSOP

VSON

Error:

Clamp condition

22




Feature Description (continued)7.3.1.9 Error DetectionThe PGA280 is designed for high dc precision and universal use, but the device also allows monitoring of signalintegrity. The device contains an input switch network for signal tests and sense points that can indicate criticalconditions. These added features support fully automated system setup and diagnostic capability. Out-of linearrange conditions are detected and stored in the Error Status Register (Register 4) until reset. The input switchesshown in Figure 44 can be used to short the input to GND, disconnect the signal, insert a 100µA test current,discharge external capacitance, and switch to a ground (VSON)-referenced signal measurement to observe thesignal at the pin (versus the differential measurement). Figure 49 illustrates the diagnostic points available forerror detection in the device architecture.

All switches are controlled through the SPI. The error signals can be combined using a logic OR function to anoutput pin and eventually be used as an error interrupt signal. Errors are normally latched, unless the LTD bit(latch disable) is set.

The error sensors are filtered with a suppression delay (Register 11). These error signals are normallysuppressed during the buffer (BUFA) active time.

NOTE: The signal path is observed for possible limitations; flags are stored and indicated in Register 4.

Figure 49. Diagnostic Points for Error Detection


23




Feature Description (continued)7.3.2 Error Indicators

7.3.2.1 Input Clamp Conduction (ICAerr)The input clamp protects the precision input amplifier from large voltages between the inputs that occur from afast signal slew rate in the input. This clamp circuit pulls current from the input pins while active. Current flowingthrough the clamp can influence the signal source and cause long settling delays on passive signal filters. Thecurrent is limited by internal resistors of approximately 2.4 kΩ. Dynamic overload can result from the differencesignal as well as the common-mode signal.

The input clamp turns on when the input signal slew rate is faster than the amplifier slew rate (see the ElectricalCharacteristics specification) and larger than ±1V. Appropriate input filtering avoids the activation. However,transients from MUX switching, internal switches, and gain switching action cannot be filtered; therefore, to avoidthese transients, activate the current buffer (BUF). The buffer isolates the signal input from the clamp, andtherefore avoids the current pulse (see Figure 44).

7.3.2.2 Input Overvoltage (IOVerr)The input amplifier can only operate at high performance within a certain input voltage range to the supply rail.The IOVerr flag indicates a loss of performance because of the input voltage or the amplifier output approachingthe rail.

7.3.2.3 Gain Network Overload (GAINerr)The gain setting network is protected against overcurrent conditions that arise because of an improper gainsetting. The current into the resistors is proportional to the voltage between both inputs and the internal resistor;a low resistor value results in high gains. This error flag indicates such an overload condition that is the result ofan improper gain setting.

7.3.2.4 Output Amplifier (OUTerr)The output stage is monitored for signal clipping to the supply rail and for overcurrent conditions.

7.3.2.5 CheckSum Error (CRCerr)SPI communication can include a checksum byte for increased data integrity, when enabled. A feature that isespecially useful for an isolated SPI. This error detection is only active with the checksum activated. See theChecksum section for details.


CS to PGA280CS

SCLK

SDI

SDO

GPIO

PGA280 3-State

CPOL = 1

0xC1 Data to external device

ECS(1)

24




7.4 Device Functional Modes

7.4.1 GPIO Operation ModeThe six GPIO port pins can be configured individually in several modes: as inputs or outputs; a special CS mode;and a connection to the PGA280 internal special function register that contains control signals or indications. SeeTable 1 for details. The GPIO can be accessed through SPI as soon as supply voltage is connected to DVDDand DGND.

Input: Standard CMOS high-impedance input, no internal termination. Terminate externally if not used or set tooutput. Note: The GPIOs are all set as inputs after a device reset.Output: Push-pull output. Output current is derived from DVDD and from DGND. Avoid I/O activity and highcurrent during high-precision measurements to avoid coupled noise.

Special Function I/O: The configuration allows connecting a designated pin to the special function register(Register 12): OSCout, SYNCin, BUFAout, BUFTin, EFout, MUX2, MUX1, and MUX0. The pin must beconfigured as an input or output according to the pin function.

Example (CHKsum not enabled):0x480B GPIO0, GPIO1. and GPIO3 set to output0x4C0B GPIO0 and GPIO1 connected to MUX0 and MUX1, EFout connected to GPIO3. MUX0 and MUX1are controlled from Register 0.

7.4.1.1 CS ModeA special CS mode for the GPIO extends the device communications to other external SPI devices, such as dataconverters or shift registers. This CS function is intended for SPI communication using four isolation couplers. Touse this mode, follow this procedure:

Configure the desired GPIO pins as outputs in Register 8, then configure the respective ECS (extended CS)bits in Register 9.

Register 2 allows control of the clock mode by CPn (n for the individual ECS pins). CP = 1 asserts ECS after thelast negative SCLK edge of the command; CP = 0 asserts ECS after the positive SCLK, as Figure 50 shows.

Use the CS command 1100 0cccb [ccc = CS coded for 0 to 7] to activate ECS on a single GPIO pin.

Example for ECS on pin GPIO1 (CHKsum disabled):0x4802 GPIO1 configured output (Note: GPIO may output a previously stored state; default is all zeroes)0x4902 Assign CS (ECS) mode to GPIO10xC1 Single byte command to activate CS on GPIO1

(1) CPn = 0; the red edge applies if CPn = 1.

Figure 50. Timing for GPIO Pin Acting as CS (ECS) to External Device


PGA280

GPIO

CS

SCLK

MOSI

MISO

CS

SCLK

SDI

SDO

CS

SCLK

SDI

SDO

CS

SCLK

SDI

SDO

SPI

Master

Addressing

MUX0

MUX1

MUX2

External

MUX

A/D

Converter

Shift Register

or DAC

Extended Chip-Select External MUX Control

OR

25




Device Functional Modes (continued)This CS pin (ECS) stays low as long as CS to the PGA280 is held low. The PGA280 SDO is turned to a high-impedance output (and requires external termination). The PGA280 ignores both clock and data signals duringthis time. Therefore, data can be read and written to another device selected by the ECS port. Communication isterminated by setting CS (to the PGA280) to high; this toggle also sets the port ECS to high and terminates theI/O transfer with the other device.

Figure 50 shows the timing for the GPIO-generated ECS pulse in clock mode SPOL = 1 (SCLK is high after CSasserts low). Register 2 allows activating SPOL = 0 by writing a 1 to the CP bit, according to SPI mode1. Theinitial setting is SPOL = 1.

Mode1; set bit to 1: a positive edge of SCLK follows after ECS asserts low (CP = 0). See the red edge of theGPIO trace in Figure 50.

Mode2; set bit to 0: a negative edge of SCLK follows after ECS asserts high (CP = 1). See the black edge of theGPIO trace in Figure 50.

The negative edge of SCLK senses data. The positive edge of SCLK sets data on the data out line (ifapplicable).

For SPI modes 0 or 3, SCLK must be inverted to indirectly sense data with the positive edge of SCLK. Figure 51shows an example of connecting additional SPI devices, addressed by the ECS. The OR connection for SDOcan be a wired-OR if all devices provide a 3-state output option with the respective device CS (ECS) set high.

The SPI interface allows clock rates higher than 10 MHz. Clock rates less than 10 MHz are recommended whenusing the ECS mode for less critical printed circuit board (PCB) layout and timing. Observe delays and distortiongenerated from isolation couplers. External drivers may be required to drive long and terminated cables.

With only four isolation couplers (digital galvanic isolation) connected in the SPI wires, the SPI can providegalvanic isolation for input and output channels. Figure 51 shows a block diagram of how to connect SPI devicesselected by the ECS (extended CS) signal.

Isolation couples or long SPI cables in harsh industrial environment are sensitive to impairments. For improvedcommunication integrity, the communication can be extended with a checksum byte.

Figure 51 shows an example of the GPIO pins used for both the extended chip select and special functions.

The chip select (CS) is connected to the PGA280 alone. The serial data input (SDI) and the serial clock (SCLK)are shared connections, and are connected to all devices [PGA280, A/D converter, and the shift register ordigital-to-analog converter (DAC)]. The serial data output comes from each of the devices and are OR-connectedor sent to an OR gate, to be received by the master. An OR gate is only required if the connected devices do notsupport 3-state operation. The PGA280 provides a 3-state output if not active. Pullup resistors may be required.

As mentioned previously, the GPIO pins are used to control an external multiplexer. In Figure 51, the three pinsfrom GPIO0, GPIO1, and GPIO2 are used as a MUX address. Two other GPIO pins are used as ECS to enablecommunications with other slave devices.

Figure 51. Example for Connecting Two Additional SPI Devices Selected by ECS


26




7.5 Programming

7.5.1 SPI and Register DescriptionThe serial peripheral interface uses four wires: CS (input), clock (SCLK, input), data in (SDI, or slave data input),and data out (SDO, or slave data output) and operates as a slave.

CS is active low; data are sampled with the negative clock edge. CS is insensitive to the starting condition ofSCLK polarity (SPOL = 1 or 0). See Figure 52 and Figure 53.

The SPI communicates to the internal registers, starting with a byte for command and address, and followed by asingle data byte (exception: 11tx 0ccc requires no data byte). The communication can include a checksum byte.When enabled, this byte follows the last valid byte. Either power on reset or software reset (SftwrRst) disablesthe checksum mode. Writing to Register 11 enables or disables checksum mode.

On a read command, the device responds with the data byte and the checksum byte. If the checksum is notdesired, setting CS to high terminates the transmission.

Multiple commands can be chained by holding CS low and sending the additional commands after the checksumbyte (if checksum is disabled, send a dummy byte). In this mode, read and write instructions can be mixed.

This interface allows clock rates up to 16 MHz. Such high clock rates require careful board layout, short wirelengths, and low parasitic capacitance and inductance. Observe delays and distortion generated from isolationcouplers. External drivers may be required to drive long and terminated cables.

7.5.2 Command Structure and Register OverviewBit 7 is the most significant bit (MSB); bit 0 is the least significant bit (LSB). Binary numbers are denoted with b'.aaaa' is used to denote the encoded register pointer, 0000b to 1111b. T denotes the buffer trigger bit. Writing tounassigned bits is ignored; however, best practice is to write a 0 for all unassigned bits. PGA280 registers,addresses, and functional information are summarized in the register map shown in (Table 1.

7.5.2.1 Command Byte01T0 aaaa dddd dddd: Write

Write 'dddd dddd' to internal PGA280 register at address aaaa

1000 aaaa 0000 0000: ReadRead from specified internal PGA280 register at address aaaa [no BUFT on read]. The number of trailingzeros provides the clock for reading data. 16 SCLK pulses are required when reading the data byte pluschecksum.

00T0 aaaa:Factory-reserved commands.

11T0 0ccc: Direct CS CommandControls CS to pin (all pins are CS-capable, but not simultaneously; only one at a time) for ccc = 0 to 6,corresponding to GPIO0 to GPIO6, if CS mode is activated.

Within the command byte, T = 1 triggers the current buffer (BUF). Each command is terminated with setting CSto high; commands can be chained within a period of CS active low, but require a checksum byte, or a dummybyte when checksum mode is disabled.

NOTEBUF cannot be triggered during a read command.

Here are several examples (discrete commands):Read Register 3:Send 0x8300; response: 0xzz19 (this value is the initial setting of BUFTIM).The first byte zz contains the line state (3-state) of SDO. The second byte is data.


Z Z ZDO7 DO6 DO5 DO4 DO3 DO2 DO1 DO0

X X X X X X X XCB7 B6 B5 B4 A3 A2 A1 A0

SDO

SDI

SCLK

CS

GPX

Sampled Here

Z Z Z

D7 D6 D5 D4 D3 D2 D1 D0C7 C6 C5 C4 A3 A2 A1 A0

SDO

SDI

SCLK

CS

GPX

Sampled Here

27




Programming (continued)

NOTEThe PGA280 sends the CHKsum, if clocks are available while CS: Send 0x830000.Response: 0xzz1937

Write Register 0:Send 0x4018; set gain to 1V/V.Write Register 4:Send 0x44FF; reset all error flags.Read Register 4:Send 0x8400; response: 0xzz00 (no error flags set).

7.5.2.2 Extended CSThe PGA280 can generate an extended chip select (ECS) for other devices that are connected to the same SPIwires: SDO, SDI, and SCLK. This ECS signal redirects the SPI communication to the connected device, whilethe PGA280 ignores data and SCLK. The CS signal to the PGA280 must stay low during such communication;as soon as CS returns high, SPI communication is terminated. See the GPIO Operation Mode section for details.

7.5.2.2.1 SPI Timing Diagrams (Read and Write)

(SCLK—Data—CS)

Figure 52. Write (to Device) Timing (GPX: Command Decoding); No Checksum Enabled.With Checksum, Command Decoding Occurs After 24th Falling Edge of SCLK

Figure 53. Read (From Register) Timing (GPX: Command Decoding); No Checksum Enabled.Falling Edge of SCLK Controls Logic


GPIO6

GPIO5

GPIO4

GPIO3

GPIO2

GPIO1

GPIO0

GPO/ECS6/OSCout

GPO/ECS5/BUFout

GPO/ECS4

GPO/ECS3/EFout

GPO/ECS2/MUX2

GPO/ECS1/MUX1

GPO/ECS0/MUX0

GPI/SYNCin

GPI

GPI/BUFTin

GPI

GPI

GPI

GPI

28




Programming (continued)7.5.2.2.2 GPIO Pin Reference

As shown in Figure 54, the PGA280 has seven multi-function pins labeled GPIO0 through GPIO6. These pinscan function as general purpose input-output (GPIO) pins either to read a digital input or to output a digital signalas an interrupt or control. GPIO functions are controlled through Register 5 and Register 8.

These pins can also be programmed to have additional special functions for the PGA280. Each of these sevenpins can be used as an output for the extended chip select function (ECS), using the PGA280 to redirect the SPIcommunications to other connected devices. CS Configuration Mode is enabled through Register 9. Additionally,Register 2 controls the clock polarity (CP) of each ECS. For each bit set to 1, a positive edge of SCLK followsCS (CP = 0); for each bit set to 0, a negative edge of SCLK follows CS (CP = 1).

Together with the GPIO and ECS functions, the seven pins can perform more specialized input and output tasksas controlled by Register 12, the Special Functions Register.

GPIO0, GPIO1, and GPIO2 can be used to control an external multiplexer. If the MUX function is enabled in thefirst three bits of Register 12, the output value on the MUX pins is controlled through Register 0. Thisconfiguration allows for simultaneous control of the PGA280 gain and external multiplexer settings by writing to asingle register.

GPIO3 can be used to output an error flag. As with bit 3 of Register 4, this option would be the logical OR of theerror bits in Register 10 (IARerr, ICAerr, OUTerr, GAINerr, and IOVerr).

GPIO4 can be used as an input to trigger the current buffer. The low-to-high edge of a pulse starts the buffer witha delay of three to four clock cycles. If held high, the buffer [BUFA] remains active. The active time is extendedby a minimum of three to four clock cycles in addition to the time set with FLAGTIM.

GPIO5 can be configured as an output to indicate a buffer active condition. The polarity is controlled by BUFApolof bit 5 in Register 10.

GPIO6 can be configured as either an output or an input with the Special Functions Register. With Bit 7,OSCOUT connects the internal oscillator to GPIO6. With Bit 6, SYNCIN allows an external oscillator to providethe master clock to the PGA280.

To use any of these functions, Register 8 must first be set to 0 for input or to 1 for an output (for GPIO, ECS, orspecial function).

Once set, any 1s in Register 9 supersede the GPIO function for the related pin, allowing for CS configuration.

Likewise, any 1s in Register 12 supersede the GPIO function and CS configuration, allowing for any of the pin-specific special functions to operate.

Figure 54. Special Function to Pin Assignment Reference


29




Programming (continued)7.5.2.2.3 Checksum

SPI communication can be secured by adding a checksum byte to the write and read data. If this mode isactivated by setting CHKsumE (bit 0 in Register 11), the PGA280 expects a valid checksum; otherwise, thedevice ignores the received data and sets CHKerr in Register 4. This event may require a Register 4 read aftereach write completes. The PGA280 always responds to a read with checksum if sufficient SCLK pulses (16) areprovided after the command byte.

A straight checksum (ignore carry) with a starting value of 0x9B, an 8-bit byte, is used. Polynomial value: 10011010b = 0x9B (b denotes binary, 0x denotes hex coding)

Write to device: Command byte + Data byte + CHKsum byteCHKsum = Polynomial value + Command byte + Data byte*;

Read command to device = Command byte + CHKsum byte

Response: Data byte + CHKsum byteCHKsum = Polynomial value + Command byte + Data byte

*The command for activating the CS on a GPIO pin (after configuration) is only a command byte: 11Tx 0ccc.Example: 0xC15C. This instruction activates CS on GPIO1. The 5C is the checksum [(0x9B + 0xC1) mod0x100 = 0x5C]

The checksum is calculated only for the communication to or from the PGA280. In extended SPI mode, ifconnecting the CS (ECS) for other SPI devices to the PGA280 port, the external device has to provide its ownchecksum character, if available.

Examples:0x4101DD Send Reset [CHKsum calculation: (0x9B + 0x41 + 0x01) mod 0x100 = 0xDD]0x4B11F7 Activate CHKsum bit 0 of Register 11. Note that activation of the CHK bit requires properChecksum.0x8B260000 Read Configuration Register 11 (contains 0x11) [0x9B + 0x8B = 0x26]0x1137 Response includes the CHKsum [0x9B + 0x8B + 0x11 = 0x37]0x44FFDF Reset all error flags in Register 4 [0x9B + 0x44 + 0xFF = 0xDF]0x841F0000 Read Register 4 [0x9B + 0x84 = 0x1F]0x001F No errors indicated if 00 [0x9B + 0x84 + 0x00 = 0x1F]

Commands can be chained while CS is active low; all bytes are added for checksum:

Examples:0x4C 07 EE; Activate MUX0, MUX1, and MUX2 to GPIO0, GPIO1, and GPIO2, respectively0x64 FF FE 40 1B 59 80 D9 00 00; Write to Register 4 with BUF trigger and reset all error flags: Write to Register 0 and set gain 1 V/V; MUX0 and MUX1 set high: Read Register 0, provide 16 SCLKs


BUFASDI

SCLK

CS

2.5 s/divm

5V

/div

30




Programming (continued)7.5.3 GPIO ConfigurationRegister priority: If GPIO pins are used, follow this procedure:

First, configure individual I/O bits as either inputs or outputs (Register 8); 0 = input, 1 = output. Bits B0 to B6are connected to GPIO0 to GPIO6, respectively.Then, configure individual bits to the desired function. When configuring for output, set the Data Register(Register 5) first to avoid glitches.

To configure the GPIO pins for the CS function (see Register 9):• Configure ECS (0 = disable, 1 = enable). If set to 1 and the I/O configuration is set to output as well, this pin

becomes ECS. Details of this configuration are described in GPIO Operation Mode, CS Mode.• Configure for clock polarity (CP), relative to ECS in Register 2; see Register 9. Set this bit to 0: a negative

edge of SCLK follows ECS (CP = 1). Set this bit to 1: a positive edge of SCLK follows ECS (CP = 0).• Configure for special function (Register 12): Special function signals can be assigned to the GPIO pins in this

manner: 0 = disable, 1 = enable. Pins xxout must be configured as outputs, and xxin must be configured asinputs in Register 8.

• GPIO data to force (Register 5) GPIO data (1 = low, 0 = high). Forcing a bit, which is assigned to a specialfunction, may be stored until GPIO is enabled.

NOTEData may be stored in internal registers and therefore may show on a given GPIO pinafter the configuration is changed.

7.5.4 Buffer TimingThe buffer is used to isolate fast transients from the overload protection of the high-precision amplifier. The bufferavoids current into the overload clamp. Fast transients result from the switching transient of a signal multiplexeror a gain change; these transients cannot be filtered in the signal path.

The buffer can be turned on by software using the T bit in the SPI command or by activating a GPIO pin. The on-time of the buffer is set in Register 3 (BUFTIM).

If controlled by software command, the buffer turns active (indicated by BUFA shown in Figure 55) with the lastfalling edge of SCLK.

Controlling an external MUX through Register 0 activates the GPIO pins after the rising edge of CS, providing anextra delay.

Alternatively, the buffer can be controlled by GPIO4, after configuration (Register 8, bit 4 = 0, and 0x4C10). Arising edge triggers the buffer with a delay of three to four clock cycles. If held high, the buffer [BUFA] remainsactive. The active time is extended by a minimum of three to four clock cycles plus FLAGTIM.

The buffer active condition can be observed at GPIO5, after configuration for output and special function(0x4820, 0x4C20). The time reference is the end of CS. The buffer is turned on with the 16th falling edge of theSCLK and writing to Register 0 (0x6018). BUFA stays high for 6 μs (BUFTIM0) after CS.

Figure 55. BUFA Timing



31



(1) Blank register bits are ignored and undefined.(2) Registers 13 to 15 are for test purposes; read-only.(3) Power-on reset values are SftwrRst values.(4) Details for GPIO pin assignments are shown in Figure 54.

7.6 Register Map

Table 1. Register Map (1)

REGISTER(Decimal,[Hex]) (2)

aaaa(Binary) R/W B7 B6 B5 B4 B3 B2 B1 B0 DESCRIPTION RESET VALUES(3)

0 0000 W/R G4 G3 G2 G1 G0 MUX2 MUX1 MUX0 Gain and optional MUX register 0000 0000b

1 0001 W SftwrRstNote2x Write-only register, soft reset, write 1 0000 0000b

2 0010 W/R C